This invention relates generally to semiconductor processing, and more specifically, to gate dielectrics of semiconductors.
In semiconductor processing, a gate electrode lying over a gate dielectric is typically formed of polysilicon. The gate electrode is usually doped with boron to increase the conductivity of the gate electrode. During subsequent processing at temperatures greater than approximately 900 degrees Celsius, the boron diffuses through the gate dielectric to an underlying semiconductor substrate, undesirably making the underlying semiconductor substrate more conductive. The increased conductivity of the underlying semiconductor substrate, which is typically silicon, decreases the performance of a semiconductor device.
Typically, the gate dielectric is silicon dioxide (SiO2). Due to the scaling of semiconductor devices, however, SiO2 is being replaced with high dielectric constant (high-k) materials, where the dielectric constant is greater than approximately the dielectric constant of SiO2 Since the high-k materials being proposed for the gate dielectric, especially hafnium oxide (HfO2), are generally less amorphous than SiO2 the high-k materials permit more boron to diffuse through the high-k material to the semiconductor substrate. Therefore, a need exists for a gate dielectric that has a high dielectric constant and substantially prevents boron diffusion from the gate electrode to the semiconductor substrate.